When two wireless devices communicate with each other in a cellular radio network in a traditional manner, each wireless device communicates radio signals with a serving base station of the radio network by sending uplink radio signals to the base station as well as receiving downlink radio signals from the base station. This is the traditional way of communication in a radio network also when the two wireless devices are located somewhat close to one another and being served by the same base station. Recently, techniques have been developed to enable such wireless devices in a radio network to communicate radio signals with each other directly, as controlled by the radio network and using frequency spectrum licensed to the network, such that each wireless device receives and decodes the actual radio signals that are transmitted from the opposite, or “peer”, wireless device. Bluetooth is another example of direct communication between wireless devices, although without control or involvement by any network.
Communication of radio signals may thus take place directly between the two wireless devices without the radio signals being communicated over the radio network via one or more base stations. In that case, the serving base station allocates radio resources, e.g. defined by time and/or frequency, which the wireless devices are allowed to use in the direct communication. Such direct radio communication between two wireless devices is commonly referred to as “Device-to-Device, D2D, communication” which term will be used throughout this disclosure.
In the field of cellular radio technology, the term “wireless device” is usually used and will be used in this disclosure to represent any wireless communication entity capable of radio communication with a cellular radio network including receiving and sending radio signals. Another common term in this field is “User Equipment, UE” which implies that the communication entity can be carried and operated by a human user, examples include mobile telephones, tablets and laptop computers. However, a wireless device in this context is not necessarily operated by a human user. It could also be a machine-to-machine type of device operating automatically such as a sensor, counter or measuring entity.
Further, the term “base station”, sometimes also referred to as a network node, radio node, e-NodeB, eNB, NB, base transceiver station, etc., represents any node of a cellular radio network that is arranged to communicate radio signals with wireless devices. The base station described here may, without limitation, be a so-called macro base station or a low power base station such as a micro, pico, femto, Wifi or relay node, to mention some customary examples. Throughout this disclosure, the terms “network node” and “User Equipment, UE” can further be used instead of base station and wireless device, respectively.
The above D2D communication may thus be employed whenever the two wireless devices, also referred to as “peer devices” or just “peers”, are close enough to one another to be able to receive and decode direct radio signals from the opposite peer. Thereby, it may be possible to reduce transmit power in the area and also to reduce interference, as compared to what is required to enable a serving base station to communicate radio signals with the wireless devices in the traditional manner.
However, there are several different modes of operation available that can be selected for the D2D communication, as schematically illustrated in FIG. 1. For example, the wireless devices D1 and D2 may communicate radio signals directly over a D2D link 100 on dedicated radio resources that are reserved exclusively for the D2D communication and cannot be used for other wireless devices in the cell, or on reused radio resources that are not reserved exclusively for the D2D communication but may be used for other wireless devices in the cell at the same time.
Another possibility is to employ so-called network assisted D2D communication where the base station BS applies Network Coding, referred to as NWC, on data that is transmitted in a radio signal between the devices D1, D2. In this mode of operation, the base station BS receives data e.g. from device D1 on a cellular radio link 102a and transmits the data in network coded form to device D2 on another cellular radio link 102b, thereby enabling the receiving wireless device D2 to use the network coded form of the data for decoding the radio signal from device D1.
However, it is a problem to know whether the operation mode of D2D communication with NWC can provide an improvement or not as compared to other operation modes. For example, D2D communication with NWC may in some circumstances require more transmit power and/or give rise to more interference than other operation modes would do under such circumstances.